In a typical electrical distribution system, electrical energy is generated by an electrical supplier or utility company and distributed to consumers via a power distribution network. The power distribution network is the network of electrical distribution wires which link the electrical supplier to its consumers. Typically, electricity from a utility is fed from a primary substation over a distribution cable to several local substations. At the substations, the supply is transformed by distribution transformers from a relatively high voltage on the distributor cable to a lower voltage at which it is supplied to the end consumer. From the substations, the power is provided to industrial users over a distributed power network that supplies power to various loads. Such loads may include, for example, various power machines or computer/electronic equipment.
At the consumer""s facility, there will typically be an intelligent electronic device (xe2x80x9cIEDxe2x80x9d), such as an electrical energy/watt-hour meter, connected between the consumer and the power distribution network so as to measure quantities such as the consumer""s electrical consumption or electrical demand. Such a meter may be owned by the consumer and used to monitor and control consumption and report costs or may be owned by the utility and used to monitor consumption and report revenue.
IED""s include devices such as Programmable Logic Controllers (xe2x80x9cPLC""sxe2x80x9d), Remote Terminal Unit (xe2x80x9cRTUxe2x80x9d), meters, protective relays and fault recorders. Such devices are widely available that make use of memory and microprocessors and have limited remote reporting capabilities. A PLC is a solid-state control system that has a user-programmable memory for storage of instructions to implement specific functions such as Input/output (I/O) control, logic, timing, counting, report generation, communication, arithmetic, and data file manipulation. A PLC consists of a central processor, input/output interface, and memory. A PLC is typically designed as an industrial control system. An exemplary PLC is the SLC 500 Series, manufactured by Allen-Bradley in Milwaukee, Wis.
A meter, is a device that records and measures electrical power consumption. Energy meters include, but are not limited to, electric watt-hour meters. In addition, meters are also capable of measuring and recording power events, power quality, current, voltages waveforms, harmonics, transients or other power disturbances. Revenue accurate meters (xe2x80x9crevenue meterxe2x80x9d) are revenue accuracy electrical power metering devices which may include the ability to detect, monitor, or report, quantify and communicate power quality information about the power which they are metering. An exemplary revenue meter is model 8500, manufactured by Power Measurement Ltd, in Saanichton, B.C. Canada.
A protective relay is an electrical device that is designed to interpret input conditions in a prescribed manner, and after specified conditions are met, to cause contact operation or similar abrupt change in associated electric circuits. A relay may consist of several relay units, each responsive to a specified input, with the combination of units providing the desired overall performance characteristics of the relay. Inputs are usually electric but may be mechanical, thermal or other quantity, or a combination thereof. An exemplary relay is type N and KC, manufactured by ABB in Raleigh, N.C.
A fault recorder is a device that records the waveform resulting from a fault in a line, such as a fault caused by a break in the line. An exemplary fault recorder is IDM, manufactured by Hathaway Corp in Littleton, Colo.
IED""s can also be created from existing electromechanical meters or solid-state devices by the addition of a monitoring and control device which converts the mechanical rotation of the rotary counter into electrical pulses. An exemplary electromechanical meter is the AB1 Meter manufactured by ABB in Raleigh, N.C. Such conversion devices are known in the art.
In the early 1980""s, the Computer Business Manufacturers Association (CBEMA), which is now the Information Technology Industry Council (ITIC), established a susceptibility profile curve to aid manufacturers in the design of power supply protection circuits. This power quality curve has since become a standard reference within the industry measuring all types of equipment and power systems and defines allowable disturbances that can exist on the power lines. Additionally, the semiconductor industry has established its own standard SEMI F47 curve for power quality, which is similar to the CBEMA curve but instead is focused on semiconductor power quality and associated supporting equipment.
In more recent years the electric utility marketplace has moved towards deregulation where utility consumers will be able to choose electrical service providers. Until now, substantially all end users purchased electric power they needed from the local utility serving their geographic area. Further, there was no way for utilities to guarantee the same reliability to all consumers from the utility because of different connection points to the transmission and distribution lines. With deregulation it is essential for consumers to be able to measure and quantify power reliability from their suppliers in order to ensure they are receiving the service they have opted for. Such service may involve various pricing plans, for example on volume, term commitments, peak and off-peak usage or reliability.
Power reliability is typically measured by several various indices. These indices include System Average Interruption Frequency Index (xe2x80x9cSAIFIxe2x80x9d), Customer Average Interruption Duration Index (xe2x80x9cCAIDIxe2x80x9d), System Average Interruption Duration Index (xe2x80x9cSAIDIxe2x80x9d), Average System Availability Index (xe2x80x9cASAIxe2x80x9d) and Momentary Average Interruption Duration Index (xe2x80x9cMAIFIxe2x80x9d). Each index provides a measure, in terms of ratios or percentages, of interruptions in delivery of electrical power, wherein an interruption may be classified as a complete loss of electrical power or where the quality of the delivered electrical power falls below or exceeds a pre-determined threshold. SAIFI measures the ratio of the total number of customer interruptions to the total number of customers served, hence the average. Lower averages signify better reliability. CAIDI measures the total customer hours interrupted to the total customer interruptions, in minutes. The lower the measure, the better the reliability. SAIDI measures the ratio of customer hours interrupted to total customers served, in minutes. Again, the smaller the number the better the system. ASAI is a ratio of total number of customer hours the electric service has been turned on to the number of customer hours the service has been demanded. It is measured as a percentage and the higher the percentage, the better the reliability. The MAIFI measurement considers interruptions that last less than 5 minutes. System Average RMS Variation Frequency Index (xe2x80x9cSARFIxe2x80x9d) is another power quality index that provides counts or rates of voltage sags, swells and/or interruptions for the system. There are two types of SARFI indicesxe2x80x94SARFI_x and SARFI_curve.
SARFI_x corresponds to a count or rate of voltage sags, swells and/or interruptions below a threshold where SARFI_curve corresponds to a rate of voltage sags below an equipment compatibility curve, such as a CBEMA or SEMI curve. Mean Time Between Failure (xe2x80x9cMTBFxe2x80x9d) is another measurement to indicate reliability. MTBF is usually expressed in hours and is calculated by dividing the total number of failures into the total number of operating hours observed. For example a device may specify MTBF as 300,000 hours. If this device operates 24 hours a day, 365 days a year it would take an average of 34 years before the device will fail.
Today""s networked economy has demanded a fundamental change in the standards by which acceptable electric power reliability is measured. In modern high technology industries, where a power interruption or deviance of even a few milliseconds can cause significant problems and lost resources, a power reliability measurement with an increased resolution is needed. Further, in today""s deregulated market, a standard reliability specification based on this higher resolution reliability measurement is needed. One such specification which standardizes higher resolution reliability measurement, involves a method of measuring reliability by the use of xe2x80x9cninesxe2x80x9d, and is stated as a percentage of time the power is available and meeting a specified quality threshold.
A typical power distribution system, for example, provides xe2x80x9cthree ninesxe2x80x9d reliability, meaning the power is available 99.9% of the time. Fully reliable xe2x80x9chigh ninesxe2x80x9d power is becoming increasingly recognized as an essential element of business survival and the traditional reliability measurements on which the industry depends are no longer sufficient for today""s technology as a measurement of downtime in minutes is no longer sufficient when only a few seconds, or even a few milliseconds, of downtime can result in large economic impact. CAIDI, SAIDI, ASAI and MAIFI do not allow a high enough resolution of time measurement for calculating reliability where events as short as 1 second may cause equipment downtime. Further, these traditional indices, are a function of aggregate loads and multiple locations, and do not provide the capability to measure reliability at single location. MTBF is usually related to a physical device, such as a generator, and not the power system attached to it and SARFI is measured in events, not in units of time. Many private corporations, such as SurePower Corporation, located in Danbury Conn., offer products such as the Sure Power System that guarantees high nines reliability. However, as technology becomes more integrated in our society a need for the consumer or utility to measure and monitor reliability coming from either the power distribution system, or a device such as the Sure Power System, is required.
Further, with the advent of electrical power deregulation, a standardized specification for power reliability is necessary to facilitate uniform comparison of suppliers. The above mentioned reliability measurements, because they necessarily measure different quantities, fail to provide such a uniform method of specifying reliability.
Therefore, in view of the above it is a primary object of the invention to provide an intelligent electronic device, more specifically an electricity measurement device, which provides more accurate reliability monitoring and more useful reliability reporting for consumers operating devices requiring high power reliability.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to an intelligent electronic device (xe2x80x9cIEDxe2x80x9d) capable of measuring and reporting the reliability of an electrical power distribution network. The IED comprises a first interface operative to couple the IED with an electrical power distribution network and a measurement component coupled with the first interface. The measurement component is operative to measure one or more parameters of the electrical power distribution network, including disturbance time, total system downtime and total system runtime. The IED further includes a reliability processor coupled with the measurement component and operative to receive the one or more parameters and compute a reliability value of the electrical power distribution network as a closest integer value to       "LeftBracketingBar"                  log        10            ⁢              (                                            Disturbance              ⁢                              xe2x80x83                            ⁢              Time                        +                          Total              ⁢                              xe2x80x83                            ⁢              System              ⁢                              xe2x80x83                            ⁢              Downtime                                            Total            ⁢                          xe2x80x83                        ⁢            System            ⁢                          xe2x80x83                        ⁢            Runtime                          )              "RightBracketingBar"    .
The IED also includes a reporting module coupled with the reliability processor and operative to receive the reliability value and report the reliability value as an indication of the reliability of the power distribution network.
The preferred embodiments further relate to a method for use with an intelligent electronic device (xe2x80x9cIEDxe2x80x9d) coupled with an electrical power distribution network to measure and report the reliability of the electrical power distribution network. The method comprises: measuring one or more parameters of the electrical power distribution network, the one or more parameters including disturbance time, total system downtime and total system runtime; computing a reliability value of the electrical power distribution network as a closest integer value to       "LeftBracketingBar"                  log        10            ⁡              (                                            Disturbance              ⁢                              xe2x80x83                            ⁢              Time                        +                          Total              ⁢                              xe2x80x83                            ⁢              System              ⁢                              xe2x80x83                            ⁢              Downtime                                            Total            ⁢                          xe2x80x83                        ⁢            System            ⁢                          xe2x80x83                        ⁢            Runtime                          )              "RightBracketingBar"    ;
and reporting the reliability value as an indication of the reliability of the power distribution network.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.